1. Field of the Invention
The present invention relates to a thermal bubble type angular accelerometer, and relates more particularly to a thermal bubble type angular accelerometer that uses radio frequency identification, Bluetooth as well as zigbee technologies on the flexible substrate for communication and can be manufactured using low temperature processes.
2. Description of the Related Art
Small angular accelerometers based on different measuring principles have been developed to meet the requirements of measuring angular acceleration. One small angular accelerometer has an ingenious structure, such as a comb structure or a vibratory structure, formed using a semiconductor wafer. By measuring the change of parasitic capacitance or resonant frequency during the rotation of the microstructures, the angular velocity or the inclined angle of the microstructures can be calculated. However, these microstructures always deform when they are under the influence of force, resulting in fatigue and aging. Therefore, the angular accelerometer with such microstructures has a short lifespan.
Another type of angular accelerometer is configured to measure an inclination angle by detecting the movement of a thermal bubble. Such a thermal bubble accelerometer is usually built on a silicon wafer and uses a silicon dioxide layer to support the heaters and the thermistors of the angular accelerometer. Because silicon dioxide has low thermal conductivity (1.5 W/(m−K)), heat transfer in the accelerometers is adversely affected so that the temperature of the lower portion of a gas chamber is low, resulting in poor sensitivity of the thermistors. In addition, the poor heat transfer also affects the sensitivity of the thermistors in response to acceleration. Thus, in order to increase the sensitivity, traditional accelerometers need greater energy supply, increasing the working temperature in the accelerometers. However, under high working temperature, the silicon dioxide support for supporting the heaters and the thermistors may expand and shrink when the accelerometer is turned on and off, resulting in material fatigue and aging, reducing the lifespan of the accelerometer.
Furthermore, traditional accelerometers are filled with air or volatile liquids used as a thermally conductive medium. However, air contains oxygen, which may oxidize the heaters, and if volatile liquid is used, the volatile liquids may chemically react with the components in accelerometers, lowering their measurement accuracy after the accelerometers have been operated for a while, and reducing the lifespan of the accelerometers.
In summary, traditional angular accelerometers have short lifespans due to their easily aged microstructures, and require high temperature processes during manufacture, along with other shortcomings such as high cost, high energy consumption, material oxidation, aging, and low performance. Therefore, a new angular accelerometer is required.